Ionomer resins are frequently used as the base resin for forming the cover of modern golf balls because the ionomer resins have improved durability, cut resistance and resilience or rebound and are easy to work.
However, golf balls using ionomer resins as the cover base resin still leave room for further improvement in rebound performance and flight distance. In particular, many users complain to the manufacturer of their request to drive the ball farther even a little. There is a need to have a golf ball having higher rebound performance and better flight performance.
To meet such a demand, acrylic acid base ionomer resins having higher rebound performance have been used as the cover base resin. See JP-B 4-49426, Japanese Patent Nos. 3,047,919, 3,119,858, 2,979,272, 3,257,739 and JP-A 9-225068. These patents use as the cover base resin a blend of an acrylic acid ionomer resin neutralized with a monovalent ion such as sodium ion and an acrylic acid ionomer resin neutralized with a divalent ion such as zinc ion, or a blend of a binary acrylic acid ionomer resin and a ternary acrylic acid ionomer resin.
However, the ionomer resin neutralized with a divalent ion like zinc ion is poor in appearance as compared with the ionomer resin neutralized with a monovalent ion like sodium ion. The use of a ternary acrylic acid ionomer resin is effective for softening at the substantial sacrifice of resilience.
For this reason or other, it is desired to have a cover material based on a binary acrylic acid ionomer resin neutralized with a monovalent ion, but a cover material capable of meeting durability as well has not been developed.